JP2014145278A - Exhaust purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purification device for an internal combustion engine which optimizes fuel supply amount during forced regeneration.SOLUTION: An exhaust purification device for an internal combustion engine comprises: a diesel particulate filter (DPF) 16 which collects PM; an exhaust temperature sensor 19 which detects an exhaust temperature; capacitance detection units 17a, 17b and 21 which detect capacitance of the DPF 16; an accumulation amount estimation section 22 which estimates a PM accumulation amount of the DPF 16 on the basis of the capacitance; and filter regeneration units 13 and 23 which can execute forced regeneration. The filter regeneration units 13 and 23 executes the forced regeneration when the exhaust temperature reaches a temperature threshold in a state where the PM accumulation amount reaches an accumulation amount threshold on the basis of the accumulation amount threshold smaller than an upper limit PM accumulation amount and the temperature threshold with which the accumulated PM can be burned and removed with a limited fuel supply amount.

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device including a filter that collects particulate matter in exhaust gas discharged from the internal combustion engine.

  For example, a diesel particulate filter (hereinafter referred to as DPF) is known as a filter that collects particulate matter (hereinafter referred to as PM) in exhaust gas discharged from a diesel engine. Yes.

  Since the DPF has a limit in the amount of collected PM, it is necessary to perform forced regeneration by periodically burning and removing the accumulated PM. Forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst upstream of the exhaust by in-pipe injection or post-injection, and raising the temperature of the exhaust gas to the PM combustion temperature by the heat generated by oxidation. Is called.

  For example, in Patent Document 1, the PM accumulation amount is estimated based on the pressure difference between the upstream and downstream sides of the DPF, the operation time (or the operation distance), and the forced regeneration is performed when the PM accumulation amount exceeds a predetermined amount. An exhaust purification device that performs the above is disclosed.

Japanese Patent No. 4070687

  By the way, the flow rate of the exhaust gas flowing through the DPF varies depending on the operating state of the engine. For this reason, the differential pressure sensor that detects the differential pressure upstream and downstream of the exhaust of the DPF may not be able to accurately estimate the PM deposition amount. In addition, in the forced regeneration start control based on the operation time (or the operation distance), there is a possibility that the forced regeneration is executed in a state where the temperature of the exhaust gas is low. Therefore, in order to raise the low temperature exhaust gas to the PM combustion temperature, it is necessary to secure a large amount of fuel supply, which may lead to deterioration of fuel consumption.

  The present invention has been made in view of these points, and an object thereof is to improve the estimation accuracy of the PM accumulation amount and to optimize the fuel supply amount during forced regeneration.

  In order to achieve the above-described object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of the internal combustion engine, a filter that collects particulate matter in the exhaust gas, and an exhaust upstream side of the filter. An exhaust temperature detecting means provided in the exhaust passage for detecting the exhaust temperature, a capacitance detecting means for detecting the capacitance of the filter, and collected on the filter based on the detected capacitance. Deposit amount estimating means for estimating the amount of deposited particulate matter, filter regeneration means capable of performing forced regeneration by supplying fuel to the filter and raising the temperature of the filter to the combustion temperature of the particulate matter; The filter regeneration means includes a deposition amount threshold smaller than an upper limit deposition amount of the particulate matter, and a predetermined high amount capable of burning and removing particulate matter deposited up to the deposition amount threshold even if the fuel supply amount is suppressed. Exhaust temperature Based on the equivalent temperature threshold, with the amount of the deposit has reached the deposition amount threshold that is estimated, the exhaust gas temperature is detected and executes the forced regeneration to reach the temperature threshold value.

  In addition, when the forced regeneration by the filter regeneration unit is not continuously executed for a predetermined time, a correction unit that corrects the temperature threshold value low may be further provided.

  Further, the capacitance detection means may include a pair of electrodes that are disposed opposite to each other with at least one partition wall in the filter and form a capacitor.

  Further, the exhaust passage on the upstream side and the downstream side of the filter is connected to bypass the filter, and the particulate matter in the exhaust gas that is provided in the bypass passage and flows through the bypass passage. And a second filter for collecting, and the pair of electrodes may be arranged to face each other with at least one partition wall interposed in the second filter.

  Further, when the forced regeneration of the second filter is executed, the pair of electrodes may function as a heater.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is possible to improve the estimation accuracy of the PM accumulation amount and optimize the fuel supply amount during forced regeneration.

1 is a schematic overall configuration diagram showing an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention. It is a figure which shows the map which estimates PM deposition amount from an electrostatic capacitance in the exhaust gas purification apparatus of the internal combustion engine which concerns on one Embodiment of this invention. In the exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention, (a) shows a change in the amount of accumulated PM, and (b) shows a change in the exhaust temperature. It is a flowchart which shows the control content by the exhaust gas purification apparatus of the internal combustion engine which concerns on one Embodiment of this invention. It is a typical whole block diagram which shows the exhaust gas purification apparatus of the internal combustion engine which concerns on other embodiment.

  Hereinafter, an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b. Further, the exhaust passage 12 is provided with an exhaust pipe injection device 13, an exhaust temperature sensor 19, and an exhaust aftertreatment device 14 in order from the exhaust upstream side.

  The exhaust pipe injection device 13 injects unburned fuel (HC) into the exhaust passage 12 in response to an instruction signal output from the ECU 20. In addition, when using the post injection by the multistage injection of the engine 10, this in-pipe injection device 13 may be omitted.

  The exhaust temperature sensor 19 detects the temperature of the exhaust gas flowing in the exhaust passage 12 upstream of the exhaust aftertreatment device 14. The exhaust temperature EGT detected by the exhaust temperature sensor 19 is input to an electronic control unit (hereinafter referred to as ECU) 20 that is electrically connected.

  The exhaust aftertreatment device 14 is configured by arranging an oxidation catalyst 15 and a DPF 16 in order from the exhaust upstream side in a case 14a.

  The oxidation catalyst 15 is formed by, for example, supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When the unburned fuel (HC) is supplied by the in-pipe injection device 13 or post injection, the oxidation catalyst 15 oxidizes this to raise the temperature of the exhaust gas.

  The DPF 16 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the exhaust gas flow direction, and alternately plugging the upstream side and the downstream side of these cells. . The DPF 16 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and performs so-called forced regeneration that burns and removes the PM when the PM accumulation amount reaches a predetermined amount. The forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst 15 by the exhaust pipe injection device 13 or post injection, and raising the DPF 16 to the PM combustion temperature (for example, about 600 ° C.).

  In addition, the DPF 16 of the present embodiment is provided with a pair of electrodes 17a and 17b that are disposed to face each other with at least one partition wall therebetween to form a capacitor. The pair of electrodes 17a and 17b are electrically connected to the ECU 20, respectively.

  The ECU 20 performs various controls such as fuel injection of the engine 10 and the exhaust pipe injection device 13, and includes a known CPU, ROM, RAM, input port, output port, and the like. In addition, the ECU 20 includes a capacitance calculation unit 21, a PM accumulation amount estimation unit 22, a regeneration control unit 23, and a threshold correction unit 24 as some functional elements. Each of these functional elements will be described as being included in the ECU 20 which is an integral hardware, but any one of these may be provided in separate hardware.

  In the present embodiment, the capacitance calculation unit 21 and the electrodes 17a and 17b constitute the capacitance detection means of the present invention. Further, the regeneration control unit 23 and the exhaust pipe injection device 13 (or a fuel injection device (not shown) of the engine 10) constitute the filter regeneration means of the present invention.

  The capacitance calculating unit 21 calculates the capacitance C between the electrodes 17a and 17b based on signals input from the pair of electrodes 17a and 17b. The electrostatic capacity C is calculated by the following formula 1, which is the dielectric constant ε of the medium between the electrodes 17a and 17b, the area S of the electrodes 17a and 17b, and the distance d between the electrodes 17a and 17b.

The PM accumulation amount estimation unit 22 calculates the PM accumulation amount PM _DEP collected by the DPF 16 based on the capacitance C calculated by the capacitance calculation unit 21. For example, when conductive carbon is deposited between the electrodes 17a and 17b, the distance d between the electrodes 17a and 17b is substantially shortened and the capacitance C is increased. Further, when PM is deposited in the medium between the electrodes 17a and 17b, the capacitance C increases as the dielectric constant ε increases. That is, there is a proportional relationship between the capacitance C and the PM deposition amount PM _DEP, and if the capacitance C is calculated, the PM deposition amount PM _DEP can be easily estimated. The ECU 20 stores a map (see FIG. 2) showing a proportional relationship between the capacitance C and the PM deposition amount PM _DEP created in advance by experiments or the like. The PM deposition amount estimation unit 22 reads the PM deposition amount PM _DEP corresponding to the capacitance C calculated by the capacitance calculation unit 21 from this map.

The regeneration control unit 23 controls forced regeneration of the DPF 16 based on the exhaust gas temperature EGT input from the exhaust gas temperature sensor 19 and the PM accumulation amount PM _DEP estimated by the PM accumulation amount estimation unit 22. More specific control contents will be described with reference to FIG.

The ECU 20 includes a first regeneration execution threshold value THV ₁ indicated by a broken line A in FIG. 3A and a second regeneration execution threshold value THV ₂ indicated by a broken line B in FIG. ), An exhaust gas temperature threshold THV ₃ (temperature threshold of the present invention) indicated by a broken line C in FIG. 3B is stored in advance. The first regeneration execution threshold THV ₁ corresponds to the upper limit accumulation amount of PM that can be collected in the DPF 16. The second regeneration execution threshold THV ₂ corresponds to a PM accumulation amount that can suppress the fuel supply amount when forced regeneration is performed in an operation state where the exhaust gas temperature EGT is a predetermined high temperature (for example, about 400 ° C.). It is smaller than the reproduction execution threshold THV _1. The exhaust temperature threshold THV ₃ is set to a high exhaust temperature (for example, about 400 ° C.) at which the PM accumulated up to the _second regeneration execution threshold THV ₂ can be removed by combustion even if the fuel supply amount is suppressed when performing forced regeneration. Equivalent to.

When the PM accumulation amount PM _DEP reaches the first regeneration execution threshold value THV ₁ (PM _DEP ≧ THV ₁ ), the regeneration control unit 23 performs forced regeneration regardless of the exhaust gas temperature EGT (FIG. 3 (a), ( Refer to time T3 in b)). Further, the regeneration control unit 23, when the PM accumulation amount PM _DEP is equal to or greater than the second regeneration execution threshold value THV _{2 and} less than the first regeneration execution threshold value THV ₁ (THV ₂ ≦ PM _DEP <THV ₁ ), Is the exhaust temperature threshold THV ₃ or more (EGT ≧ THV ₃ ), the forced regeneration is executed (see times T1 and T2 in FIG. 3B). On the other hand, even if the PM accumulation amount PM _DEP satisfies the condition of the second regeneration execution threshold value THV ₂ or more and less than the first regeneration execution threshold value THV ₁ (THV ₂ ≦ PM _DEP <THV ₁ ), the exhaust temperature EGT is the exhaust temperature. When the threshold value is less than THV ₃ (EGT <THV ₃ ), forced regeneration is suspended (see times T 1 and T 2 on the broken line Y in FIG. 3B). That is, when the exhaust gas temperature EGT is low, the forced regeneration is forgotten, and when the exhaust gas temperature EGT rises due to a change in the operation state thereafter, the forced regeneration is executed. Thereby, the fuel supply amount at the time of forced regeneration can be effectively suppressed.

The threshold correction unit 24 corrects the exhaust temperature threshold THV ₃ based on a time during which forced regeneration is not continuously performed (hereinafter referred to as a regeneration non-execution period T _NRE ). In the present embodiment, the regeneration non-execution time T _NRE is calculated by integrating the time counted by the timer counter from when the ignition key is turned ON (including when forced regeneration ends). The ECU 20 stores in advance an upper limit time T _MAX that allows the forced regeneration not to be performed. When the regeneration non-execution time T _NRE exceeds the upper limit time T _MAX (T _NRE > T _MAX ), the threshold correction unit 24 corrects the exhaust temperature threshold THV ₃ to be low. As a specific correction method, for example, the maximum value (see α in FIG. 3B) of the exhaust gas temperature EGT during the forced regeneration non-execution period is stored, and the exhaust gas temperature threshold value THV _{3 is set} to this maximum value. It is preferable to correct downward.

  Next, based on FIG. 4, the control flow by the exhaust emission control device of the present embodiment will be described. Note that this control starts simultaneously with the ON operation of the ignition key.

In step (hereinafter, the step is simply referred to as S) 100, it is determined whether or not the PM accumulation amount PM _DEP estimated from the capacitance C has reached the _second regeneration execution threshold value THV2. When the PM accumulation amount PM _DEP is equal to or greater than the _second regeneration execution threshold value THV ₂ (YES), the control proceeds to S110. On the other hand, when the PM accumulation amount PM _DEP is less than the _second regeneration execution threshold value THV ₂ (NO), this control is returned.

In S110, it is determined whether or not the PM deposition amount PM _DEP estimated from the capacitance C has reached the _first regeneration execution threshold value THV1. When the PM accumulation amount PM _DEP is equal to or greater than the _first regeneration execution threshold value THV ₁ (YES), the control proceeds to S120, and forced regeneration is performed regardless of the exhaust gas temperature EGT, and the process returns. On the other hand, when the PM accumulation amount PM _DEP is less than the _first regeneration execution threshold value THV ₁ (NO), the present control proceeds to S130.

In S130, the exhaust gas temperature EGT whether reaches the exhaust temperature threshold value THV ₃ is determined. When the exhaust gas temperature EGT is equal to or higher than the exhaust gas temperature threshold value THV ₃ (YES), the control proceeds to S140, and forced regeneration is executed and the process returns. On the other hand, if the exhaust temperature EGT is less than the exhaust temperature threshold THV ₃ (NO), the control proceeds to S150. That is, forced regeneration is suspended.

In S150, it is determined whether the reproduction non-execution time T _NRE has exceeded the upper limit time T _MAX . When the reproduction non-execution time T _NRE exceeds the upper limit time T _MAX (YES), the control proceeds to S160. On the other hand, when the reproduction non-execution time T _NRE is equal to or shorter than the upper limit time T _MAX (NO), this control is returned.

In S160, performs correction to reduce to a maximum value of the stored exhaust gas temperature EGT exhaust temperature threshold value THV ₃ between S100～150, the control is returned. Thereafter, each control step of S100 to S160 is repeatedly executed until the ignition key is turned off.

  Next, functions and effects of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment will be described.

  In the conventional forced regeneration, the forced regeneration start control is performed based on the DPF differential pressure and the operation time. However, since the exhaust gas flow rate changes with the operating state, there is a possibility that the PM accumulation amount cannot be accurately estimated from the DPF differential pressure. In addition, in the forced regeneration start control based on the driving time (or driving distance), forced regeneration may be executed even when the exhaust temperature is low, and the fuel consumption may deteriorate due to an increase in the fuel supply amount. .

On the other hand, the exhaust emission control device of this embodiment estimates the PM deposition amount PM _DEP from the capacitance C between the pair of electrodes 17a and 17b provided in the DPF 16. Further, even if the estimated PM accumulation amount PM _DEP reaches the second regeneration execution threshold value THV ₂ , forced regeneration is forgotten when the exhaust gas temperature EGT is low (less than THV ₃ ), while the exhaust gas temperature EGT reduces the fuel supply amount. When a high temperature state (THV ₃ or more) that can be suppressed is reached, forced regeneration is performed.

Therefore, according to the exhaust gas purification apparatus of the present embodiment, the PM accumulation amount PM _DEP can be estimated with high accuracy and the fuel supply amount can be suppressed based on the capacitance C that is not affected by the change in the operating state. By suspending forced regeneration until a high exhaust temperature (THV ₃ or higher) is reached, fuel efficiency can be effectively improved.

The exhaust purifying apparatus of the present embodiment, when the forced regeneration is not performed continues for a predetermined period of time is configured to correct a low exhaust gas temperature threshold value THV _3.

  Therefore, according to the exhaust emission control device of the present embodiment, forced regeneration can be reliably performed even under use conditions where the frequency of high-load operation is low and the exhaust temperature EGT does not become high.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, as shown in FIG. 5, a bypass passage 18 that bypasses the DPF 16 may be connected to the exhaust passage 12, and the bypass passage 18 may be provided with a measurement DPF 16 a (second filter) having a small capacity. In this case, it is preferable that the pair of electrodes 17a and 17b are arranged opposite to each other with at least one partition wall in the measurement DPF 16a, and an orifice 18a (throttle) for adjusting the flow rate of the exhaust gas is provided in the bypass passage 18. . Further, when the forced regeneration of the measurement DPF 16a is executed, a voltage may be applied to the pair of electrodes 17a and 17b so as to function as a heater.

DESCRIPTION OF SYMBOLS 10 Engine 12 Exhaust passage 13 Exhaust pipe injection apparatus 14 Exhaust after-treatment apparatus 15 Oxidation catalyst 16 DPF (filter)
19 Exhaust temperature sensor 20 ECU
21 Capacitance calculation unit 22 PM deposition amount estimation unit 23 Regeneration control unit 24 Threshold correction unit

Claims (5)

A filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
An exhaust temperature detecting means provided in an exhaust passage upstream of the filter for detecting the exhaust temperature;
Capacitance detecting means for detecting the capacitance of the filter;
A deposition amount estimating means for estimating a deposition amount of the particulate matter collected by the filter based on the detected capacitance;
Filter regeneration means capable of performing forced regeneration by supplying fuel to the filter and raising the temperature of the filter to the combustion temperature of the particulate matter,
The filter regeneration means includes
A deposition amount threshold smaller than the upper limit deposition amount of particulate matter, and a temperature threshold corresponding to a predetermined high exhaust temperature at which particulate matter deposited up to the deposition amount threshold can be burned and removed even if the fuel supply amount is suppressed. An exhaust gas purification apparatus for an internal combustion engine, wherein forced regeneration is executed when the detected exhaust gas temperature reaches the temperature threshold value in a state where the estimated accumulation amount has reached the accumulation amount threshold value. The exhaust emission control device for an internal combustion engine according to claim 1, further comprising correction means for correcting the temperature threshold to be low when forced regeneration by the filter regeneration means is not continuously executed for a predetermined time. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the electrostatic capacitance detection means includes a pair of electrodes that are disposed to face each other with at least one or more partition walls in the filter and form a capacitor. A bypass passage that bypasses the filter by connecting the exhaust passage upstream and downstream of the filter;
A second filter that is provided in the bypass passage and collects particulate matter in the exhaust gas flowing through the bypass passage;
The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the pair of electrodes are disposed to face each other with at least one partition wall interposed in the second filter. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein when the forced regeneration of the second filter is executed, the pair of electrodes function as a heater.